In order to improve the dimensional stability of end-grained wood upon environmental humidity variations, a two-step procedure was thoroughly Studied which involved the osmotic impregnation of native ... [more ▼]

In order to improve the dimensional stability of end-grained wood upon environmental humidity variations, a two-step procedure was thoroughly Studied which involved the osmotic impregnation of native poplar wood by PEG, followed by the reactive impregnation with HMDI, leading to polymer chain extension and polyurethane formation. It came out that the efficiency of PEG and/or polyurethane grafting within ligno-cellulosic cell walls was intimately related to parameters such as concentration of the PEG impregnation bath, PEG molar mass, time and temperature of impregnation steps. Based on the different sample characterizations, Soxhlet extraction and density measurements, it came out that adequate experimental conditions are to carry out osmotic impreanation at 20degreesC for 24 h starting from an aqueous solution of PEG([PEG] = 0.5mol(.)L(-1) and (M) over bar (nPEG) = 400 or 1000) and reactive impregnation in bulk with a large excess of HMDI at 20degreesC for 2 h. Combining scanning electron microscopy and mercury porosimetry demonstrated the selective impregnation of cell wall and wood rays which were collapsed in native wood and expanded in wood polyurethane composites. [less ▲]

Time-resolved small-angle X-ray scattering (SAXS) measurements performed during the formation of tetraethyl orthosilicate (TEOS) based silica gels in alcohol with 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS) as an additive are reported. The measurements reveal no discontinuity of the nanostructure at the gel point. A chemically induced spinodal phase separation is found to give a coherent picture of the collected data. Increasing the amount of EDAS induces the phase separation on a smaller length scale, which finally leads to a modified gel morphology. The SAXS measurements and the electron micrographs associated with the dry gels could be interpreted in terms of the suggested wet gel formation mechanism. [less ▲]

Despite commonly accepted ideas, evaporative drying does not always completely destroy the pore texture of phenolic gel. This work shows that very porous carbon materials can be synthesized by evaporative ... [more ▼]

Despite commonly accepted ideas, evaporative drying does not always completely destroy the pore texture of phenolic gel. This work shows that very porous carbon materials can be synthesized by evaporative drying and pyrolysis of aqueous resorcinol-formaldehyde gels provided that the operating variables are correctly chosen. Moreover, in this manner monoliths can be easily produced. The pore texture of the materials was studied before and after pyrolysis in order to determine which synthesis and/or pyrolysis variables have an influence on the final texture of the carbon. Results show that it is possible to tailor the morphology of these materials by varying the initial pH of the precursors solution in a narrow range. Micro-macroporous, micro-mesoporous, microporous or totally non-porous carbon materials were obtained. The specific surface area is independent from the initial pH whereas the total void volume varies from 0.4 to 1.4 cm(3)/g when the initial pH decreases from 6.25 to 5.45. These materials can be used as catalysts supports or for electrochemical applications, the texture control being an interesting advantage. (C) 2004 Elsevier Ltd. All rights reserved. [less ▲]

The pore texture of carbon materials obtained from evaporative drying and pyrolysis of resorcinol-formaldehyde aqueous gels is controlled by the initial pH of the precursors solution. In order to produce ... [more ▼]

The pore texture of carbon materials obtained from evaporative drying and pyrolysis of resorcinol-formaldehyde aqueous gels is controlled by the initial pH of the precursors solution. In order to produce transition metal-containing carbons with tailored texture, various metallic salts were dissolved in the precursors solution. When necessary, a complexing agent (HEDTA or DTPA) was added to render the metal ions soluble. Ni, Fe and I'd loaded carbon xerogels were synthesized and their pore texture was studied after evaporative drying and after pyrolysis. The carbon texture was also studied with regard to the nature of the metal and the amount of complexing agent. The solubilization of transition metal salts in the resorcinol-formaldehyde aqueous solution does not prevent the texture regulation, even though this texture control is influenced: the limits of the pH interval leading to micro mesoporous carbon materials can slightly differ when a metal salt and/or a complexing agent are added. The pH range shift depends mainly on the amount and nature of the complexing agent, but also slightly on the nature of the metal ion. Nevertheless, the metal particles obtained are rather big (diameter > 15 nm). For catalytic applications, the metal dispersion must be enhanced, especially in the case of expensive metals. (C) 2004 Elsevier Ltd. All rights reserved. [less ▲]

Two poly(L-lactide-co-epsilon-caprolactone) random copolymers containing 5 and 40 mol% of epsilon-CL, namely P(LA-co-CL5) and P(LA-co-CL40), respectively, have been made macroporous by freeze-drying ... [more ▼]

Two poly(L-lactide-co-epsilon-caprolactone) random copolymers containing 5 and 40 mol% of epsilon-CL, namely P(LA-co-CL5) and P(LA-co-CL40), respectively, have been made macroporous by freeze-drying solutions in dimethylcarbonate. Most of the freeze-dried foams, prepared by varying polymer concentration and cooling rate, exhibited two main pore populations: (1) longitudinally oriented tube-like macropores with diameters greater than or equal to100 mum, and (2) interconnected micropores (10-100 mum). Pore characteristics, including macropore density, mean diameter, and interdistance, as well as micropore density, area, and shape, were determined by image analysis of scanning electron micrographs in order to study the influence of processing and formulation parameters on foam structure and properties. The pore orientation and the 3-D texture also were studied by image analysis and impedance spectroscopy. In the case of the P(LA-co-CL5), the macropore diameter increased with the cooling rate while the micropore diameter decreased. The micropores also became more circular when the cooling rate was increased. The pore size and morphology of the P(LA-co-CL40) were quite unchanged by varying the cooling rate. All the other conditions being the same, the P(LA-co-CL5) foams were better organized than the P(LA-co-CL40) foams, and pore orientation was improved at the higher cooling rate. Pore size and morphology also can be controlled by changing the polymer concentration (Cp), as we showed by studying P(LA-co-CL5) foams prepared by freeze-drying solutions in the 1-10 w/v% Cp range. Macropore density, average diameter, and interdistance of P(LA-co-CL5) foams increased with Cp, but the micropore characteristics remained almost unchanged no matter the Cp. The reliability of the characterization methods has been discussed, with special attention to mercury intrusion porosimetry, which is used primarily for measurement of pore volume and pore size distribution. However, this technique is reported here as a destructive and unreliable method for the characterization of fragile P(LA-co-CL40) foams. This study shows that image analysis and impedance spectroscopy can give reliable information relative to the pore morphology and anisotropy of freeze-dried foams. [less ▲]

Mixtures of TEOS with substituted methoxysilanes generate low-density xerogels due to a nucleation mechanism involving the substituted alkoxysilane. The sol-gel transition of these mixtures was followed ... [more ▼]

Mixtures of TEOS with substituted methoxysilanes generate low-density xerogels due to a nucleation mechanism involving the substituted alkoxysilane. The sol-gel transition of these mixtures was followed by theological characterisation. The transition from sol to gel takes place in a few minutes at ambient temperature. For the series exhibiting nucleation by the additive. the gel time goes through a slight minimum when the ratio of additive/main reagent increases. The elastic modulus increases with increasing ratio of additive/main reagent as the particle size decreases because of the nucleation mechanism by the additive. Samples with smaller particles exhibit the highest modulus for equal silica concentrations. (C) 2003 Elsevier Science B.V. All rights reserved. [less ▲]

Evaporative drying of polyurethane-based gels produces xerogels. Supercritical drying after replacement of interstitial liquid by supercritical CO2 produces aerogels. SEM micrographs show that both materials are made up of small size particles gathered up in filament-shaped, strongly cross-linked aggregates. Density measurements show that they both have a large pore volume. When submitted to mercury porosimetry, the behavior of these materials is similar to that of inorganic aerogels, as previously observed. Mercury does not penetrate the pore network, but the whole material is densified. The usual Washburn equation cannot be used to analyze the mercury porosimetry. A well-suited equation based on a buckling model of filament-shaped aggregates has been developed in order to determine the pore volume distribution of mineral dried gels. This equation is also valid for analyzing the texture of organic hyperporous materials like polyurethane dried nanoporous gel. (C) 2003 Elsevier Science Ltd. All rights reserved. [less ▲]

Secondary sludges from two different wastewater treatment plants are conditioned and dewatered in the same way before drying in a lab-scale convective rig at the same operating conditions. Several ... [more ▼]

Secondary sludges from two different wastewater treatment plants are conditioned and dewatered in the same way before drying in a lab-scale convective rig at the same operating conditions. Several techniques are used to characterize the texture of the dried materials over a wide range of scales from nm up to mm. Texture and porosity of the dried products are studied by SEM imaging, nitrogen absorption isotherms (0.5 < d(p) < 50 nm), mercury porosimetry (7.5 nm < d(p) < 150 mum) and X-ray microtomography (spatial resolution= 41 mum). The image analysis of cross-sections reconstructed by microtomography also allows following shrinkage and textural evolution during drying. [less ▲]

For easier handling and use in fixed bed reactors, Pd-Ag/SiO2 aerogel-like xerogel catalysts were shaped into microspheres using the microencapsulation process developed by BRACE GmbH. Before the bead ... [more ▼]

For easier handling and use in fixed bed reactors, Pd-Ag/SiO2 aerogel-like xerogel catalysts were shaped into microspheres using the microencapsulation process developed by BRACE GmbH. Before the bead production process, the xerogel catalyst was ground in water and mixed with ethylene glycol and sodium alginate, the latter of which is the gelation agent. The beads were formed at a vibrating nozzle and solidified during their fall in a water tank containing calcium ions, which induce cross-linking of the alginate and consequent bead hardening. Preliminary work was done using a syringe instead of the material-consuming BRACE unit. The beads were made from a suspension of dried only, dried and calcined, or dried, calcined, and reduced catalyst. The textural properties of the beads were analyzed by nitrogen adsorption-desorption isotherms and mercury porosimetry; and bead catalytic activity was tested for selective hydrodechlorination of 1,2-dichloroethane. The beads made from a suspension of dried catalyst appear to have properties the closest to that of the xerogel reference catalyst. Porosity and surface area are maintained at their level before bead formation. However conversion of 1,2-dichloroethane decreases after the production process, possibly due to poisoning by calcium ions. (C) 2004 Elsevier B.V. All rights reserved. [less ▲]

The purpose of this paper is to propose a method of analyzing the mercury porosimetry data in the case of materials called hyperporous. This class of material does not undergo intrusion by mercury ... [more ▼]

The purpose of this paper is to propose a method of analyzing the mercury porosimetry data in the case of materials called hyperporous. This class of material does not undergo intrusion by mercury; instead, it shrinks under the mercury isostatic pressure and its density increases. The phenomenon is partially or completely irreversible. The proposed method enables computing the pore volume distribution as a function of the pore size in the same way as Washburn's method does in the case of mercury intrusion. (C) 2002 Elsevier Science B.V. All rights reserved. [less ▲]

This study consists in verifying the coherence of a few commonly used analysis methods of nitrogen adsorption-desorption isotherms. These methods were tested on model samples obtained by mechanically ... [more ▼]

This study consists in verifying the coherence of a few commonly used analysis methods of nitrogen adsorption-desorption isotherms. These methods were tested on model samples obtained by mechanically mixing two micro- and mesoporous solids respectively with known, mass proportions. Although the individual analysis methods may lead to discrepancies in the interpretation of the isotherms, their systematic comparison allows drawing a coherent picture of the porous texture. [less ▲]

Micro- and mesopore structure modifications in silica low-density xerogels induced by additives in TEOS-based alcogels precursors are discussed on the basis of image analysis of transmission electron ... [more ▼]

Micro- and mesopore structure modifications in silica low-density xerogels induced by additives in TEOS-based alcogels precursors are discussed on the basis of image analysis of transmission electron microscopy (TEM) micrographs and nitrogen adsorption-desorption experiments. To perform image analysis, novel image processing has been developed on the basis of classical signal treatment and mathematical morphology theory. The obtained results have been correlated with classical and fractal interpretation of nitrogen adsorption-desorption measurements. [less ▲]

This paper presents an original preparation method of metal catalysts supported on carbon porous material [1]. Carbon porous materials can be synthesised by evaporative drying and pyrolysis of aqueous ... [more ▼]

This paper presents an original preparation method of metal catalysts supported on carbon porous material [1]. Carbon porous materials can be synthesised by evaporative drying and pyrolysis of aqueous resorcinol-formaldehyde gels whose operating, variables are correctly chosen. The porous texture of these materials is mainly controlled by the precursor solution pH. Texture analysis shows that it is possible to tailor the morphology of these materials : indeed, micro-macroporous, micro-mesoporous, microporous or non porous materials can be obtained by varying the pH value in a narrow pH interval. This texture control is slightly influenced by the introduction of a metal in the gel : the limits of the pH interval can slightly differ when a metal salt is added to the resorcinol-formaldehyde aqueous solution. Carbon supported nickel and palladium catalysts prepared by this method have proven to be active for ethylene hydrogenation. [less ▲]